1. Field of the Invention
The invention relates to a hydraulic device for a hydraulic drive for a high-voltage or high-tension circuit-breaker, including a drive piston for a movable contact piece having two piston sides being in connection with a high-pressure reservoir in a closed condition and being acted upon by high-pressure fluid on both sides, a switch-over valve releasing a path to the low-pressure space for the fluid in the space with the larger piston area, for the purpose of circuit-breaking, and at least one circuit-closing pilot valve and circuit-breaking pilot valve for activating the switch-over valve.
The movable contact piece of a high-voltage circuit-breaker, in particular an SF.sub.6 gas-isolated circuit-breaker, is connected to the drive piston of a drive piston cylinder configuration. The drive piston is actuated by a hydraulic configuration for opening and closing the circuit-breaker. For that purpose, the two spaces on either side of the working piston are acted upon by a fluid at high pressure. The pressure is provided by a hydraulic reservoir which can be configured as a gas reservoir or a spring reservoir. The piston area in the first space is larger than that in the second space because the piston rod is connected to the piston in the latter space. Both spaces of the drive piston and cylinder configuration are connected to a switch-over valve which releases a path for the high-pressure hydraulic fluid into a low-pressure volume.
The switch-over valve is activated hydraulically by means of pilot valves which have to be actuated electromagnetically, with circuit-breaking pilot valves and circuit-closing pilot valves being normally provided to suit the desired switching sequence. An OFF-ON-OFF switching sequence can be achieved with two circuit-breaking pilot valves and one circuit-closing pilot valve.
It is known that high-voltage circuit-breakers can only extinguish the current to be interrupted on transition through zero current. However, where a short-circuit current has to be switched off, a decaying direct current proportion is superimposed on the alternating current proportion and the switching capability of the circuit-breaker becomes greater as the direct current proportion decays.
In some cases, particularly for switch gears in the U.S.A., a delaying electrical relay is connected into the breaker circuit so as to permit an increase in the circuit-breaking power. However, for reliability reasons, circuit-breakers should be opened directly without additional possible fault elements, such as circuit-breaking relays.